The long-term objective of this research is to understand the functional basis for the expression of apolipoprotein (apo) E in peripheral tissues. ApoE is important for regulating systemic cholesterol transport and metabolism. Among the plasma apolipoproteins, apoE is unusual in being expressed in many tissues and is involved in cellular processes and diseases that are independent of systemic lipoprotein metabolism. This proposal has two primary objectives. The first is to define the mechanisms by which low-levels of plasma apoE suppress atherosclerotic lesion development. Previous studies showed that levels of transgenic apoE too low to correct hypercholesterolemia in apoE-deficient mice still blocked aortic lesion formation. The second goal is to determine how localized apoE expression in adrenocortical cells regulates the utilization of cholesterol for steroid production. These studies employ apoE-deficient mouse lines that have been engineered to express different levels of transgenic apoE selectively in the adrenal gland. The proposal has 3 Aims. Aim 1 has three goals focused on how low-levels (equal to approximately 10[-8]M) of apoE alter the initial stages of lesion formation. Goal 1 will use quantitative real-time PCR to monitor expression of a set of candidate genes during initial stages of leukocyte recruitment to the vascular wall. Goal 2 will determine whether signaling pathways for platelet derived growth factor or LFA-1 or those involving the transcription factor NFkappaB are activated in vascular cells at early stages, and whether low-level apoE alters this activation. Goal 3 will test which receptors of the LDL receptor family are important for the atheroprotective effects of low-level apoE. Aim 2 will define mechanisms by which apoE alters cholesterol utilization for steroid production in the adrenal gland in vivo. Goal 1 will use immunocytochemical approaches to evaluate the variegated pattern of transgenic apoE expression in the adrenal cortex and to test the effect of localized apoE on the expression of key proteins involved in the provision of substrate cholesterol to the steroidogenic pathway. Goal 2 will test which receptors of the LDL receptor family are important for the effects of apoE in adrenocortical cells. Aim 3 has collaborative projects to test the effects of low-level apoE on neointimal formation after arterial injury and on regression of atherosclerotic lesions. These studies will provide new mechanistic information about actions of apoE on cholesterol metabolism and atherosclerosis.